Remove MimeType related code
Summary:
This is uneeded and we can create and use the mimetype
directly inside of the DetachableTabBar as nothing else
needs to know about it.
Test Plan: Compile and runs. Unused code.
Reviewers: hindenburg, sandsmark, ngraham
Reviewed By: hindenburg
Subscribers: konsole-devel
Tags: Konsole
Differential Revision: https://phabricator.kde.org/D15378